This invention is related specifically to the air tight sealing of the coupling joint between the top of the converter and the stack while melting and refining iron. Usually this refining requires control of contamination, that is to say, the objective is to cool and clean powder from the gases generated during the refining process in the converter. In general the stack is located as close as possible to the top of the converter without regard to admission of atmospheric air. Nevertheless, air seal at the joint must be concerned about the volume of gases handled in the stack and the temperature changes affected by the combustion of air coming in the stack, and in leakage of the carbon monoxide generated in the converter.